Communication system



Sept. 7, 1943. H. J. NICHOLS v COMMUNICATION SYSTEM Filed Aug. 27, 1941 2 Sheets-Sheet 1 w M a w a. w. M f. p

0 6 w 4 1 n 2 G H? I, II C X m P lw m fl m 4 X A TTORNE Y Patented Sept. 7, 1943 UNITED STATES PATENT OFFICE COMMUNICATION SYSTEM Harry J. Nichols, Point Pleasant, N. J.

Application August 27, 1941, Serial No. 408,505

12 Claims.

The present invention relates to synchronizing systems and more particularly to synchronizing systems holding the deviation from synchronism to the narrow limits required in facsimile or television operation and is an improvement on the system, as disclosed in applicant's United States Patent 2,111,153 granted March 15, 1938.

In devices of the prior art, as disclosed, for example, in said Patent 2,111,153, the degree of deviation from synchronism has been within the tolerances permitted in telegraphy. Such tolerances, however, have permitted a greater degree of deviation from synchronism than is permitted in facsimile or television operation. For example, in the system of said Patent 2,111,153, and in all such systems wherein a rotating contactor mechanism is employed for producing compensation controlling impulses, the degree of deviation from synchronism may be such as to distribute the received synchronizing impulse between two contact segments, whereby insuflicient impulse power is distributed to the correction apparatus to permit of correction back to synchronism. Further, in such rotating contactor mechanisms, a marked deviation from synchronism is required before sufficient impulse force is delivered to the compensating apparatus, and further the amount of impulse force is proportional to the amount of deviation. In such devices, therefore, the correction force has proven insufiicient until a deviation has occurred, which is greater than the amount of deviation permitted in facsimile or television operation.

One of the objects of the present invention, therefore, is to produce a system of synchronism that will obviate these undesirable characteristics existing in the prior art.

Another object is to provide a novel synchronizing system in which a single synchronizing impulse is employed to produce a pair of efiects, and means controlled by each of said pair to produce difierent phase changing efiects which completely counteract each other when unison is established.

A further object is to provide a novel system for synchronizing, in which the period of duration of the synchronizing pulse has little or no bearing upon the compensation effect produced, the mere existence of such'a pulse, for any slight period, initiating a compensating effect, and means operable independently of the synchronizing pulse control the duration of such compensating efiects.

Another object is to provide a novel synchronizing device in which switching means, controlled by sharp cut off cam devices, are employed to precisely determine the initiation and period of duration of a compensating efiect.

Still another object is to provide novel quickacting switching mechanism producing a sharp distinction between lag and lead of a controlled rotary device with respect to the time of reception of a synchronizing pulse.

Another object is to provide a novel synchronizing system in which the degree of compensation for deviation from synchronism is independent of the degree of such deviation.

A further object is to provide a novel differential gear mechanism for producing in a. precise manner a compensating effect independent of the degree of deviation from synchronism.

Still another object is to provide a synchro nizing system comprising a first and a second rotary device, means producing repeated pulses disclose, by way of example, the principle of the.

invention and the best mode, which has been contemplated, of applying that principle.

In the drawings:

Fig. l is a purely schematic View illustrating the essential elements employed at both the sending and receiving station of one type of facsimile system and illustrating, generally only, certain mechanism employed in transmitting a synchronizing pulse.

Fig. 2 is a side View, partly in section, illustrating in greater detail the phase correction mechanism, as illustrated in Fig. 1.

Fig. 3 is a sectional view taken on line 33 of Fig. 2.

Fig. 4 is an end view illustrating the clutch mechanism of Fig. 2.

Fig. 5 is a fragmentary detailed view, illustrating the clutch disconnecting operation.

Fig. 6 is a plan view illustrating in more detail one of the elements of the cam contactor of Fig. 1.

Fig. 7 is a side view of the device of Fig. 6.

Figs. 8a, 8b and 8c are schematic views, illustrating different steps in the operation of the synchronizing control contacts, as controlled by the cam contactors of Fig. 1.

Figs. 9a to 9f. inclusive, are graphical illustrations of the sequence of operations involved in ultilizing the synchronizing pulse at the receiver for production of synchronism.

Fig. 10 is a circuit diagram of one embodiment of the synchronizing system employed for control of the starting and phase control mechanism of the present invention.

Fig. 11 is a circuit diagram of another embodiment of synchronizing system employed.

Referring to the drawings and more particularly to Fig. 1, there is illustrated schematically therein the elementsof one form of facsimile system to which the present invention may be applied and the elements employed in maintaining synchronism between a sending and a receiving station.

A drive motor M provided with a reduction gear box GB rotates at reduced speed a drive shaft a. Clutch mechanism CM controlled by a start magnet SM controls the rotation, by drive shaft 20a, of the phase correction mechanism PCM, described in detail later. 20b whose phase with respect to drive shaft 20a can be altered by operation of the phase correction mechanism, carries a drum D upon which is mounted the record or material to be scanned or A driven shaft the material upon which there is reproduced a facsimile of the record scanned.

Mounted on the drum D and extending axially thereof is a strip 2 I which in the present instance is illustrated as a black strip, outside the field of graphic material carried by the drum.

Scanning machanism is provided for scanning the record and for periodically producing and repeating a synchronizing pulse, which may comprise any well known scanning mechanism. An optical scanning mechanism is illustrated comprising a light source L, a focusing lens FL, a collector lens CL and a photocell PC. The optical mechanism can be translated axially with respect to the drum D, as indicated by the arrow. Upon rotation of drum D and axial translation of the optical mechanism, a light beam scans each elemental area of the record and also the black strip 2 I. The changes in light tonal values of the elemental areas scanned produce changes in light intensity, proportional to such changes, which changes in light intensity are transformed by the photocell into changes of an electrical quantity, in a manner well known. Such electrical changes are representative of the light tonal values of the elemental areas scanned and may be employed to modulate a carrier wave for transmission over a communication channeL'represented generally as a line, in a well known manner. The amplifier modulator AM is employed to amplify the electrical changes and to modulate the carrier.

Upon each rotation of thedrum D, the strip 2| is also scanned by the light beam to affect the photocell PC whereby electrical changes are produced which are transmitted over the line to constitute synchronizing signals. Since the strip 2I is scanned during the so-called underlap period. a time separation of the picture and synchronizing signals exists.

At the receiving station, the signals are demodulated and the synchronizing pulses are filtered from the picture signals, by any well known means, as for example by means such as dis closed in U. S. Patent No. 2,153,202. The picture signals may be employed to control mechanism well known for reproducing a facsimile of the record scanned, such reproducing apparatus not comprising any part of the present invention and therefore not being further described.

The. synchronizing pulses, preferably of the form as illustrated in Fig. 9a. are employed in a novel manner to produce complete synchronism between a transmitting drum D, at one station. and a receiving drum at another station. Since the apparatus at each station may be similar, reference is made to Fig 1 for the mechanism employed in producing synchronism.

The phase correction mechanism PCM, outlined in Fig. 1, is illustrated in greater detail in Figs. 2, 3, 4 and 5. Drive shaft 20a is driven by the motor M (Fig. 1) as described above, and carries a drive collar 22 (Fig. 2) connected to drive shaft 20a by a pin 23. The inner end perimeter of collar 22 is toothed to form a crown gear 22a which meshes, when the clutch is engaged, with the crown gear 24a (Fig. 4) of clutch sleeve 24 rotatably mounted on hub 25 of annular gear GI mounted for rotation on shaft 20a. A double fingered annular spring member 24b (see also Fig. 4) is attached to sleeve 24 by notched openings (not shown) fitted to mating projections on sleeve 24. The fingers of spring member 24!) extend in opposite directions and fit respectively between pairs of lugs 26, 26 provided on the outer face of gear GI (Fig. 4). A stop pin 24c fastened to sleeve 24 engages with the slanting surface 21 of armature 28 (Fig. 5) upon rotation of clutch sleeve 24, when the armature is released by the start magnet SM upon deenergization of the same. As the sleeve 24 continues its rotation, pin 24c rides on the surface 21 of armature 28 (Fig. 5) until it is stopped by notch 28a, the transverse motion of pin 24c axially sliding sleeve 24 to the left (Fig. 2) to disengage the crown gear surfaces 24a and 22a to thereby disengage the clutch mechanism CM. Spring member 24b provides a spring bias urging the clutch to engaged position and serves to cushion the shock when the clutch is engaged. To engage the clutch, start magnet SM is energized, as described later, to attract its armature 28 whereby the pin 240 is released and spring member 24b urges the crown gear members 24a and 22a into engagement whereby shaft 20a drives the gear GI through collar 22, sleeve 24 and spring member 24b engaging the lugs 26. Driven shaft 20b is aligned with the drive shaft 20a by a ball and socket connection 29. Mounted on shaft 202) by means of set screw 30 is an annular gear G2, similar in construction to gear GI. A third annular gear G3 is mounted for rotation on shafts 20a and 20b, intermediate gears GI and G2 and is driven by the novel epicyclic mechanism now to be described.

Mounted on driven shaft 20b and intermediate gears G2 and G3 is an epicyclic disk ED2 provided with a notched periphery (see Fig. 3). Mounted for rotation with and for rotation within the epicyclic disk ED2 is the twin pinion gear TF2, one of whose gears meshes with the annular gear G3 and the other with annular gear G2. A counterweight W2 is provided on disk ED2 to counterbalance the weight of pinion TF2. A similar epicyclic disk EDI is mounted for rotation on drive shaft 20a and is provided with counterweight WI and with the pair of twin pinion gears 'I'Pl mounted for rotation with and rotation within the epicyclic disk EDI and engaging: respectively" with annular gears GI and G3.

Mounted on base 3| is theretard maget RM controlling a pivoted armature 32 provided with atoothed end 32a biased to open position by spring 33 and abutting a stop pin 34. In the normal' or deenergized position, armature tooth 32a is free of the teeth of epicyclic disk ED2 (Fig. 2)., Upon energization of magnet RM, as

described-presently, armature 32 is attracted,

and tooth 32a engages a tooth of epicyclic disk EDI to lock the disk against rotation. The advance magnet AM is similarly constructed and mounted to lock epicyclic disk EDI upon energization of the. magnet, as described presently. As-shown in dotted outline, the bases 3I of magnets RM and AM are so mounted as to be bodily :CM; gears GI, G2 and G3 and epicyclic disks EDI and ED2 and twin pinions TPI and TP2 rotate as a unit whereby shaft b is driven by the drive shaft 20a, with no change in phase of 23b with respect to 20a. If the receiving mechanism is running slow with respect to the transmitting mechanism, the advance magnet AM is energized, as described later, its armature 32 is attracted and epicyclic disk EDI is held against rotation. Gear GI drives twin pinion TPI which in turn differentially drives G3, ED2 and G2, as a unit, so that the phase of shaft 20b is advanced with respect to shaft 20a to thereby advance the phase of the receiver drum D (Fig. 1) without altering the speed of rotation of shaft 20a. If shaft 20b is rotating in advance of the transmitting drum, epicyclic disk EDZ will be held and gears GI, TPI and G3 and disk EDI will rotate, as a unit, to rotate twin pinion TP2 and differentially drive gear G2 to retard the phase of shaft 20b. When both the advance magnet and the retard magnet are energized, both disks EDI and ED2 are held, and the shafts 20a and 20b are rotated, always in phase.

Referring to Figs. 1, 6, 7, 8a, 8b and 8c, the theory and construction of the synchronizing switch control means 'are illustrated therein. Each switch, such as the switch XI (Fig. 10), comprises a pair of spring contactors, such as SI and S2 (Fig. 8a) controlled by cams such as CI and'CI, respectively. As illustrated schematically inFigs. 8a, 8b and 8c, the spring contactors, such asSI and S2, are held in open position for nearly one complete rotation of cams CI and C2, mounted for rotation by shaft 200 (see also Fig. 1). As shaft 200 rotates, the cam CI releases spring contactor SI to engage spring contactor 82 (Fig. 8b), and switch XI is thereby closed. As cams CI and C2 continue to rotate, spring contactor S2drops away from spring contactor SI (F18.8C) and remains so disengaged until the positions of Fig. 8a are again assumed. Each of the cams CI and C2, for example, is provided with a sharp drop off surface whereby the exact point of closure and opening of a switch such as XI, is sharply determined. As illustrated in Figs. 6 and 7, cam'members CI and C2 are mounted for rotation by shaft-20c. A follower 35, pivoted on shaft "rides on the evolute surface of cam C2, for example, (Fig. 7) its insulated end 3511 engaging the spring contactor S2. Similarly, the

follower 35 of cam CI rides on the surface of cam Cl and its insulated end 350 engages spring contactor SI tomaintain springs SI and S2 in a separated condition. As follower 35 of cam CI drops off the sharp edge of cam CI (Fig. 8a), spring SI engages spring S2 to close switch XI (Fig. 8b). As cams CI and C2 continue rotation, follower 35 of cam C2 drops ofl. the sharp edge of cam C2, to disengage springs SI and S2, as illustrated schematically in Fig. 8c. The drop ofi cam surface, provides a sharp line of demarcation between the open and closed positions of the respective switches XI, etc., whereby the deviation from synchronism is sharply ascertained and the kind of deviation is also ascertained, as described presently. As shown schematically in Fig. 1, cams CI to C8, inclusive,

control the spring contactors'SI to S8, inclusive, which in pairs, suchas SI and S2, comprise the switches XI, X2, X3 and X4, respectively, (Fig. 10).

Referring to Fig. 10, there is illustrated therein, in diagrammatic form, the circuit at a receiving station for utilizing. the synchronizing pulses, according to one embodiment of the invention, to produce and maintain complete synchronism between the sending and the receiving drums D, by electrical control of the start magnet SM, advance magnet AM and retard magnet RM. The synchronizing signals and picture signals are received and demodulated and the synchronizing and picture signals are separated =by the amplifier, demodulator, filter ADF. The picture signals are employed, in any desired and well known manner, to reproduce on receiving drum D, a copy or facsimile of the record at the sending station. The synchronizing pulses, of definite duration, and preferably square-topped, as illustrated in Fig. 9a, are applied to primary P of transformer T and appear in the secondary windings SdI and 8112, as two discrete pulses of opposite polarity (see Fig. 9b) designed as el and e2, one marking the beginning of the synchronizing pulse and the other the termination thereof. It should'be particularly noted that the synchronizing signals can be comparatively prolonged compared to picture signals, facilitating diiferentiation therebetween. It is further assumed that eI can trip only, gas filled triode TI and that e2 can trip only, gas filled triode T2. Gas filled triode TI comprises a cathode, a grid GrI and an anode, the grid GrI being connected to the secondary SdI by the switch XI, comprising the spring contacts SI and S2 (Fig. 8a). The plate of TI is connected to one end of the coil of advance magnet AM, by switch X2, comprising spring contacts 83 and S4 (Fig. 911), while the other side of the coil is connected to the coil of quick acting slow-release start magnet SM, the other end of whose coil is connected to the positive side of the battery BI whose negative side is connected to the cathode of TI. A shunt circuit comprising resistor R5 and switch X5 is provided around start magnet SM, which shunt cir-, cuit is employed when the device is used as a transmitter.

The grid GrI is maintained at cut oil by means of biasing battery B2 and grid resistor RI. The grid Gr2 of gas filled triode T2 is similarly connected to secondary SdZ by switch X3 comprising spring contacts S5 and S8 (Fig. 9e) and the anode of T2 is connected by switch X4 comprising springs 81 and SB (Fig. 9f) to one end of the coil of retard magnet RM whose other side of the circuit of Fig. which is more economical of construction than the circuit of Fig. 10 but produces generally the same result. Gas. filled triodes TI and T2, of Fig. 10, are replaced by vacuum tube triodes VTI and VT2, respectively. The grid Grl of VTI is connected to the secondary Sdl through a neon lamp NLI and switch xi in series. One side of neon lamp NLI is conected by resistor R3 and switch X2 to a positive source of potential. The plate of tube VTI is connected directly to one side of the coil of advance magnet AM, and the start magnet SM is again in the common return for the plate circuits of two tubes, namely, VTI and VT2. The grid G12 of vacuum tube VT2 is connected to secondary 8d! by means of neon lamp NL2 and switch X3 in series, and positive potential is supplied to one side of neon lamp NL2 by way of resistor R4 and switch X4. The operation of the embodiment of Fig. 11 simulates the operation of the circuit of Fig. 10 but replaces the more expensive gas fllled trigger tubes Ti and T2 of Fig. 10, by ordinary triodes VTI and VT2 and the inexpensive neon lamps NLI and NL2, while still obtaining the trigger action of the gas filled tubes of Fig. 10. Briefly, the operation of the circuit of Fig. 11 is as follows: Upon closure of switches XI and X2, for example, a posittive biasing potential is applied to neon lamp NLI. Vacuum tube VTI is negatively biased,

virtually to cut oil, via battery B2. Upon receplong as neon lamp NLI is ignited. Switch XI. A

may be thereafter opened, without quenching the lamp NLI, and the flow in the plate circuit of tube VTI continues until switch X2 is opened, removing the positive bias from lamp NLI which is thereupon quenched, and the flow through the plate circuit of tube VTI ceases. The action of tube VT2 is similar, except that NL2.is ignited solely by pulse e2 at the end of the synchronizing pulse. The operation of the tubes VTI, VT2 is therefore made to simulate the operation oi the gas filled tubes Tl andT2, to control the operation of magnets AM, SM and RM, aswill be described in detail presently.

Referring to Figs. 9a to 9!, inclusive, there is illustrated graphically, the timing of the operations of the several switches XI, x2, x: and X4, with respect to the time of occurrence of the synchronizing pulse. The letter i represents the synchronizing pulse, cl and c2, (as stated above) the discrete pulses appearing in secondaries Sdl and Sd2, respectively; ti to t8, inclusive, timing points at which'the switches open or close; and Si to 88, inclusive, in pairs, such as SI and S2, for example, comprising the respective switches xi, etc.; illustrate the action of the individual spring contacts controlled by cams CI to C8, inclusive (Fig. 1). The timing charts ofFigs. 9a to if, inclusive, represent either the "start" or "unison condition.

The sequence of events, at start" is as follows: It is assumed that switches Xi and X2 (Fig. 10) are closed. so that Gri is connected to the econdary Sdl and the anode circuit of TI is closed through the coils of advance magnet AM and start magnet SM. Gas filled tube TI is biased below the trip voltage. At point ti (Figs. 9a and 9b) pulse el is applied to grid Grl. to trip Tl producing a flow of current in the plate circuit of TI to thereby energize the advance magnet AM and the start magnet SM. Upon energization of start magnet SM, its armature 28 (Fig. 2) is attracted, to release clutch sleeve 24 and permit engagement of the clutch mechanism CM, whereby the drum D at the receiving station is started'into rotation approximately in step with the drum at the sending station. Upon energization of advance magnet AM, its armsture 32 is attracted and tooth 32a engages and holds epicyclic disk EDI whereupon the diflerential action 0! the phase corrector mechanism PCM advances the phase of shaft 20b with respect to shaft 20a. Immediately after drum D at the receiver starts to rotate, cam C2, controlling spring contactor S2 (Fig. 8c) permits spring S2 to drop, thereby opening switch Xi and disconnecting grid Grl from secondary Sdl (see also Fig. 9c). Even though switch Xi is opened, current flow through the plate circuit of gas filled tube Tl continues until cam Cl allows the spring contact S4 to drop (Fig. 9d) thereby opening switch X2 in the plate circuit of TI, to quench Tl. It is seen, therefore, that the time of triggering on of tube TI is sharply defined with respect to the pulse i, but that once tube TI is triggered, the correcting effect is maintained for I fore the synchronizing pulse 1, is terminated, at

t2 (Fig. 9a), cams C5 and Cl permit spring contacts S5 (Fig. 9e) and S1 (Fig. 9!), respectively,

to drop, thereby closing switches x: and x4 (Fig. 10) to render tube T2 operative, so that pulse e2 triggers tube T2. when T2 is thus triggered, its plate current flow continues for a predetermined period (Fig. 9f) whose period is completely independent of the amount of deviation from synchronism, so that full corrections are applied, upon the slightest deviation from synchronization. As is seen in Figs. 9a to 9!, inclusive, both an advancing and a retarding effect are produced, which are equal and opposite, when the device is at unison. There is, therefore, continuously maintained, a dynamic eflect maintaining synchronism. instead of the usual static effect, which usual static effect requires a considerable change of condition before any correction eflects are applied.

On the very first revolution, after clutch mechanism 'CM is engaged; due to the slight delay caused by clutch action, inertia, etc., switches XI and K4 are not closed until after the occurrence of pulse e2, so that only an advancing phase effect is produced, which gives the mechanism a boost towards unison, to overcome the initial lag.

As is seen from Fig. 9e, at point t3, cam CO I permits spring contact 86 to drop thereby opening switch X3, and at point t, cam C4 permits switch contact 84- (Fig. 9d) to drop, to open switch X2, as described above. At point t5, cam 08 permits switch contact 88 (Fig. 9!) to drop to open switch X4, and at point t8, cams Cl and Cl permit spring contacts SI and S3 to drop thereby closing swltchesXl and X2 (Fig. and preparing tube Tl for operation by the next synchronizing pulse 1. Due to the slight delay in starting, as describedabove, it may be assumed that switches xi and X2 are in such closed Dosition, during this second synchronizing pulse, so

that advance magnet AM is again energized and magnet SM is sustained. The phase of the receivingdrum is therefore advanced'until the condition'of unison, as illustrated in Figs. 9a to 9!, inclusive, is achieved. At unison, as stated above, switches x3 and X4 close before the end of the synchronizing pulse i, discrete pulse e2, trips on T1, and the retard magnet RM is energized, whereby a phase retarding effect is produced, equal to the phase advancing effect, and the receiving drum is no longer advanced in phase but is held at unison with the sending drum. Should drum D at the receiver tend to lag, advance magnet AM only, is energized, and the phase is ad- "vanced; should drum D at the receiver tend to lead, retard magnet RM only, is energized and the phase is retarded. Synchronism is therefore continuously maintained by changing the phase of the receiving drum .0, when necessary, with out altering the speed of rotation of the driving motor M at the receiver.

By inspection of Figs. 9a to 9 inclusive, it is seen that duejto the sharp control of switches-Xi and X3, the correcting mechanism at the receiver distinguishes sharply between a lag in phase on one hand and a lead in phase on the other hand, so that not only is the corrective force quickly applied, but the proper kind of corrective force is quickly ascertained and applied. It is readily apparent, therefore, that the sharp drop off cams, controlling the control switches,'produce a sharpdiscrimination between the kind of correcrection is produced to obtain accurate control of synchronism to a degree of precision required by facsimile, and such correction .is continuously,

quickly and efficiently produced and the correction applied is completely independent of the amount of deviation from synchronism, so that a full corrective effect is applied upon the slightest deviation from synchronism.

- the phase of said one device with respect to the While there has been shown and described and 7 pointed out the fundamental novel features of the invention as applied to a plurality of embodiments, itwill be-understood that variousomis- 'sions'and substitutions and changes in the form ing said one rotary device substantially isochrovhouslywith said other device, means for advancing the phase of said one device with respect'to said other device while maintaining the speed of said drive means constant, means for retarding other while maintaining the speed of said drive means constant, means producing repeated electrical synchronizing impulses representative of a predetermined phase position of said other device, means for transmitting said impulses, means for receiving said impulses and producing a pair of eifects in response to reception of each of said impulses, a pair of gas filled triodes, means selectively applying one of said effects to the grid of one of said gas filled triooes and the other effect to the grid of the other of said triodes, means controlled by either of said triodes for rendering said drive means effective to produce approximate synchronization between said devices, means controlled by'one of said triodes for rendering said phase advancing means effective and means controlled by the other of said triodes for rendering said phase retarding means effective.

2. In a synchromzing system for control of one rotary device by another, in combination, means producing repeated electrical synchronizing impulses representative of a predetermined phase position or said other device, means for transmit;

ting said impulses, means for receiving said im-' pulses and producing a pair of effects in response to reception of each of said impulses, drive means for rotating said rotary device substantially isochronously witn said other device, means for rendering said drive means effective to Produce approximate synchronization between said devices, means for advancing the phase of said one device with respect to said other; device while maintaining the speed of said drive means constant, and means for retarding the phase of said one device with respect to said other device while maintaining the speed of said drive means constant, one of said pair of effects controlling said rendering means and one of said phasechangers, and the other of said pair controlling said rendering means and the other of said phase 'changers 3. In a system for control of one rotary device by another, in combination, means producing repeated electrical synchronizing impulses representative of a predetermined phase position of said other. device, means for transmitting said impulses, means for receiving said impulses and producing a pair of effects in re ponse to reception of* each of said impulses, ive means for rotating said one rotary device substantially isosynchronously with said other device, means for rendering said drive means efiective to produce approximate synchronization between said devices, means for altering the phase of said one device with respect to said other device while maintaining the speed of said drive means constant, means controlled by said impulses for initiating operation of said drive means and-of said altering means, means for determining the period of effectiveness of said drive means, and

means comprising asharp drop off cam for contive of a predetermined phase position of said other device, means for transmitting said impulses, means for receiving said impulses and producing a pair of effects in response to recaption of each of said impulses, a pair of triodes, a pair of gas filled tubes respectively connected to the grids of said triodes, means selectively applying one of said effects to one of said gas filled tubes and the other effect to the other tube of said pair, means controlled by either of said triodes for rendering said drive means effective to produce approximate synchronization between said devices, means controlled by one of said triodes for rendering said phase advancing means effective, and means controlled by the other triode for rendering said phase retarding means effective,

5. In a synchronizing system for control of one rotary device by another, in combination, drive means for rotating said rotary device substantially isochronously with said other device,

means forv advancing the phase of said one de- Y vice with respect to the other while maintaining the speed of said drive means constant, means for rearding the phase of said one device with respect to the other while maintaining the speed of said drive means constant, means producing repeated electrical synchronizing impulses representative of a predetermined phase position of said other device, means for transmitting said impulses, means'for receiving said impulses comprising a primary of a transformer, a secondary for said transformer, a pair of gas filled triodes, means including switching means for connecting one end of said secondary to the grid ofone of said triodes, means inc'lnding switching means for connecting the other end of said secondary to the grid of said other triode, means for rendering said drive means effective, means for rendering said phase advancing means effective and means including switching means connecting said first and second rendering means in the plate circuit of one triode, means for rendering said phase retarding means effective and means including switching means "for connecting said first rendering means and said last rendering means in the plate circuit of said other triode, and adjustable-cam means having a sharp drop off controlling said switching means, respectively, to initiate operation of said triodes under control of said impulses and to control the duration of operation of said advancing and re tarding means independently of said impulses.

6. In a synchronizing system for control of one rotary device by another, in combination, means producing repeated electrical synchronizing signals representative of a predetermined phase position of said other device, means for trammitting said signals, means for receiving said signals, means controlled by each received signal for producing two discrete impulses of opother device to maintain approximate synchronization between said devices, and means for altering the phase of said one device with respect to said other device while maintaining the speed of said drive means constant, said means comprising means controlled by said received impulses for producing a combined mechanical differential and electrical differential compensating effect.

8. In a synchronizing system for control of one rotary device by another, in combination, means producing repeated electrical synchronizing impulses representative of a predetermined phase position of said other device, means for transmitting said impulses, means for receiving said impulses, drive means for rotating said one rotary device substantially isochronously with said other device to maintain approximate synchronization between said devices, means controlled by said impulses for advancing the phase of said one device with respect to said other device while maintaining the speed of said drive means constant, means controlled by said impulses for retarding the phase of said one device with respect to said other device while maintaining the speed of said device constant, and means including switching means controlled by sharp drop off cam means sharply differentiating between a lag and a lead in said one device with respect to said other device for applying said pulses selectively to said advancing or to said retarding means.

9. Phase correcting mechanism comprising a drive shaft, a driven shaft, means for coupling said drive shaft to said driven shaft, means controlled by a synchronizing pulse for rendering said coupling means effective, a double fingered annular spring member attached to said coupling means, an annular gear, means interconnecting said gear andsaid spring member whereby said gear is rotated by said drive shaft when said pulse controls said rendering means, an epicyclic member mounted for rotation, a pair of gears mounted for rotation with and rotation within said member, a second annular gear, said pair of gears respectively engaging with said first and said second annular gears, a second epicyclic member, a pair of gears mounted for rotation with and rotation within said member, a third annular gear connected to said driven shaft, said second pair of gears engaging, respectively, with said second and third annular gears, means alternately locking and freeing said epicyclic means for rotation selectively, one of said epicyclic means producing advance of phase of said driven shaft and the other producing a retardation of the phase thereof with respect to said drive shaft.

posite polarity, and means controlled by the said discrete impulses for altering the phase of said one device, said phase altering means including differentially operable means which are responsive to, and selectively rendered effective by, the said discrete impulses of opposite polarity.

7. In a synchronizing system for control of one rotary device by another, in combination, means producing repeated electrical synchronizing impulses representative of a predetermined phase position of said other device, means for transmitting said impulses, means for receiving said impulses, drive means for rotating said rotary device substantially isochronously with said 10. Phase shifting mechanism comprising a drive shaft, a driven shaft, an annular gear driven by said drive shaft, an annular gear connected to said driven shaft for driving the same, a third annular gear intermediate said first two gears, a pair of epicyclic members, each mounted for rotation, a pair of gears mounted on each of said members for rotation therewith and rotation therein, the gears of one pair meshing, respectively, with said first and said third annular gear and the gears of said other pair meshing, respectively, with said second and said third annular gears, and means for alternately locking and releasing each of said epicyclic members for rotation to produce a change in phase of said driven shaft with respect to said drive shaft,

11. Phase shifting mechanism comprising a drive shaft, a driven shaft, a gear driven by said .drive shaft, a gear on said driven shaft for rotation thereof, a third gear intermediate said first two gears, a pair of epicyclic members, each mounted for rotation, gears carried by said members respectively and meshing with said first and second and with said second and third gears, respectively, individual means including a solenoid for locking and releasing said epicyclic members respectively upon energization and deenergization, respectively, of said solenoids and means for shifting said individual means with respect to said epicyclic members whereby said epicyclic members respectively are locked and released upon deenergization and energization, respectively, of said solenoids.

12, In a synchronizing system for control of one rotary device by another, in combination, means producing repeated electrical synchronizing impulses of sustained period representative of a predetermined phase position of said other device, means for transmitting said impulses,

means for receiving said impulses, drive means for rotating said one rotary device substantially isochronously with said other device to produce approximate synchronization between said devices, means for advancing the phase of said one device with respect to said other device while maintaining the speed of said driving means constant, means for retarding the phase of said one device with respect to said other device while maintaining the speed of said driving means constant, means producing from each of said sustained impulses a pair of practically instantaneous pulses selectively efiective to control said advancing and retarding means, and means HARRY J. NICHOLS. 

